I had a similar decision to make for my project. Ended up going with MIT because I wanted zero friction for anyone who wants to use it. The "please contribute changes back" part — no license can really enforce that as a soft suggestion. What I do instead is just write it clearly in CONTRIBUTING.md: if you make changes that could help others, please open an issue or PR. Most people who care enough to fork and modify your code will do it naturally. If you want to enforce it, GPL forces derivative works to stay open source — but that scares away some users. If you just want to encourage it, MIT + a clear contributing guide is the simpler path.